Atmospheric pollution resulting from products of combustion of hydrocarbon fuels, particularly those eminating from the exhaust of gasoline-fueled automotive internal combustion engines, is a well recognized environmental pollution problem. Much effort and research has gone into the development of vehicle engines operable on various lighter hydrocarbon fuels as an alternative to gasoline, such as ethanol, and even those fuels having less complex hydrocarbon molecules with fewer carbon atoms per molecule, i.e., pentane, butane, propane, methane, and even ethane. Natural gas (methane) has been favored because of its abundance and clean-burning performance, low cost and its well known and long use as a fuel for internal combustion engines of the stationary type. However, in order to provide an adequate "on-board" supply for fueling automotive vehicle internal combustion engines, the fuel must be stored in highly compressed form, requiring heavy duty, highly pressurized fuel tanks and fuel system components capable of storing gaseous methane at ambient temperatures ranging up to 125.degree. F. (51.6 C..degree.) and hence capable of withstanding pressures of several thousand psi. Propane on the other hand, can be stored in liquid form and at much lower pressures than methane (i.e., 0 psi at -44.degree. F.; (-42.2.degree. C.), 125 psi at about 70.degree. F.; (21.1.degree. C.) and 260 psi at 125.degree. F.; (51.6.degree. C.). In certain geographic locations supplies of liquid propane fuel for a variety of uses are already relatively abundant and economical. Therefore much attention in recent years has been devoted to developing automotive fuel systems utilizing propane as the alternative fuel of choice, even though such systems still must deal with the challenges associated with pressurized containment and delivery of such fuel.
Typical vehicle propane fuel tank systems commercially available today supply propane in gaseous form to the engine intake manifold via a carburetor fuel feeding system, and leave much to be desired in terms of fuel efficiency, safety, bulk, complexity of plumbing hardware and fuel handling components such as valve, fittings, etc. and the associated multiplicity of joint connections prone to leakage problems. Such propane fuel tank systems for automotive engine use have a bung welded onto the tank for each valve, etc. that is required. Because of the many welded joints that are required, such fuel tanks are expensive to manufacture and maintain. The potential leak paths are many due to the numerous weld joints, fluid handling components, supply line fitting connections, etc. Such systems require leak testing of their numerous individual components after assembly to a tank, adding further complexity and cost. These factors also contribute to high maintenance and service costs. The vehicle manufacturer is also saddled with relatively high assembly costs due to the variety of valves and fittings that must be threaded onto and connected to the tank and sealed securely.
Proposed EPA and DOT regulations would also be difficult to satisfy with such known systems because of environmental pollution arising from exhausting propane to atmosphere during tank filling operations. Tank overfilling and overflow, as well as the drawbacks of currently available "spit-valve" type propane tank filling equipment are also major contributors to such problems.
Such fuel systems also need to comply with many presently applicable safety standards, such as complying with "crash test" integrity standards and providing for proper evacuation of the fuel in "bonfire" tests to prevent tank rupture and explosion.
Vehicle drivability and engine performance are also important criteria which are not adequately satisfied by presently available propane fuel tank systems for vehicle engine use. So far as presently known, all such commercial systems provide propane to the engine in its gaseous state which makes it very difficult to maintain a proper fuel supply to the engine intake manifold under varying operating conditions. In addition, loss of engine power in such gaseous systems can be in the order of of 10-15%. Engine startability, particularly "hot restart", are further problems not adequately addressed by such known systems.
Until the advent of the present invention as disclosed and claimed hereinafter, so far is known many of the aforementioned problems have remained unsolved or inadequately solved, including inability to safely store on an automotive vehicle pressurized propane in liquid form, and also to safely and reliably supply such propane in liquid form to the engine intake manifold via suitably modified conventional electronically controlled liquid fuel injectors under all engine and vehicle operating conditions in an economical manner while achieving satisfactory engine vehicle performance comparable to gasoline powered vehicles.